Static pressure air bearing

ABSTRACT

In order to provide a static pressure air bearing having two axes usable in a vacuum environment in which the connection of the supporting air exhaust pipe does not adversely affect the motion of the bearing mechanism, air exhaust pipes are connected only with the fixed part(s) of the lower axis. Air exhaust from the upper axis is conducted through inner air exhaust piping (passages) formed within the fixed parts of the upper and lower axes, so that the exhaust pipes need not be connected with the movable parts.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] The present invention relates to a static pressure air bearinghaving two axes, a lower axis and an upper axis, used in a vacuumenvironment.

[0003] 2. Description of Related Art

[0004] Conventional static pressure air bearings having two axes used ina vacuum environment have been provided with air exhaust pipes connectedwith the movable part of each axis bearing mechanism. That is, each axishas its own dedicated air exhaust pipes, which are connected to themovable part of each axis. Therefore, air exhaust from each axis bearinghas been separately done.

[0005] The conventional air exhaust method requires, with respect to theupper axis, the connection of the air exhaust pipe with the movable partof the upper axis bearing mechanism. Additionally, a large bore diameterof the pipe is required to obtain efficient air exhaust displacement.These features cause a great resistance to the feeding motion of thebearing and seriously affect the bearing performance. This problemarises when the air exhaust pipe is connected with the movable part ofthe upper axis, and also arises when the air exhaust pipe is connectedwith inner piping formed within a fixed part of the upper axis (becausethe fixed part of the upper axis also moves).

SUMMARY OF THE INVENTION

[0006] The present invention provides a static pressure air bearinghaving two axes usable in a vacuum environment in which the connectionof the supporting air exhaust pipe does not adversely affect the motionof the bearing mechanism.

[0007] To accomplish the above and/or others objects, according to oneaspect of the present invention, there is provided a static pressure airbearing having two axes, a lower axis and an upper axis, in which innerair exhaust piping formed within a fixed part of the lower axis andinner air exhaust piping formed within a fixed part of the upper axis(which is fixed on a movable part of the lower axis) communicate witheach other.

[0008] Through the implementation of the above configuration, the airexhaust pipe can be connected only with the fixed part of the lower axisand need not be directly connected with the movable parts of the bearingmechanism. Consequently, an air exhaust pipe of a large bore diameterdoes not adversely affect the bearing performance.

[0009] In a preferred embodiment of the present invention, thecommunication between the inner air exhaust piping of the fixed part ofthe lower axis and the inner air exhaust piping of the fixed part of theupper axis is provided through air exhaust communication grooves and airexhaust communication piping formed within the movable part of the loweraxis. Through the implementation of the above configuration, the airexhaust pipe need not be connected directly with the fixed part of theupper axis. Thus, because there is no connection of the air exhaust pipewith any of the moving parts of the bearing mechanism, the air exhaustpipe does not adversely affect the bearing performance, e.g.,rectilinear feeding accuracy.

[0010] In a preferred embodiment of the present invention, thesupporting air is exhausted through the inner air exhaust piping formedwithin the fixed parts of the lower and upper axes. Through the aboveconfiguration, the air exhaust pipe need not be connected either withthe movable part of the lower axis or with the movable part of the upperaxis.

[0011] In a preferred embodiment of the present invention, air exhaustgrooves are disposed surrounding each air pad of the lower and upperaxes. Through the above configuration, because only a limited amount ofair can flow into the vacuum chamber from the gap of the bearing, thebearing is usable in a vacuum environment.

[0012] In a preferred embodiment of the present invention, air supplystructure is also accommodated in the fixed parts. That is, inner airsupply piping formed within the fixed part of the lower axis and innerair supply piping formed within the fixed part of the upper axis (whichis attached to the movable part of the lower axis) communicate with eachother. Through the above configuration, because both the air supply andthe air exhaust are done within the fixed parts, tubing connection withthe movable parts can also be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention will be described in conjunction with the followingdiagrams in which like reference numerals designate like elements andwherein:

[0014]FIG. 1 is a perspective view showing an embodiment of a staticpressure bearing mechanism according to the present invention;

[0015]FIG. 2 is a sectional view of part of the static pressure airbearing mechanism shown in FIG. 1;

[0016]FIG. 2(a) is a sectional view of the FIG. 1 static pressure airbearing mechanism;

[0017]FIG. 2(b) is a sectional view like FIG. 2(a), but shows themovable part of the upper axis moved to its left-most position;

[0018]FIG. 2(c) is a plan view of the surface of the fixed part of theupper axis, as seen in the direction of arrow C in FIG. 2(b);

[0019]FIG. 2(d) is a sectional view of the upper axis as seen in thedirection of arrow D in FIG. 2(b);

[0020]FIG. 2(e) is a sectional view of the upper axis as seen in thedirection of arrow E in FIG. 2(b);

[0021]FIG. 2(f) is a sectional view like FIG. 2(a);

[0022]FIG. 2(g) shows the upper surfaces of lower axis fixed parts asseen in the direction of arrow G in FIG. 2(f);

[0023]FIG. 2(h) is a plan view of the inner surface of the lower axismovable parts as seen in the direction of arrow H in FIG. 2(f);

[0024]FIG. 2(i) is a sectional view like FIG. 2(a);

[0025]FIG. 2(j) is a sectional view of the lower axis as seen in thedirection of arrow J in FIG. 2(i);

[0026]FIG. 2(k) is a sectional view like FIG. 2(a);

[0027]FIG. 2(l) is a sectional view of the lower axis as seen in thedirection of arrow L in FIG. 2(k);

[0028]FIG. 3 is a cross-sectional view as seen in the direction of arrowA in FIG. 2(a) of the fixed and movable parts of the upper axis;

[0029]FIG. 4 is a plan view of the inner surface of the upper axismovable part as seen in the direction of arrow B in FIG. 2(b);

[0030] FIGS. 5(a) and 5(b) are see-through views that show the relativepositions of the exhaust grooves, air pads and exhaust apertures of thefixed and movable parts of the respective upper and lower axes when themovable parts are at opposite ends of their respective ranges ofmovement;

[0031] FIGS. 5(c), 5(d) and 5(e) show the relative positions between theelements (the air pads and exhaust apertures) on the upper axis fixedpart and the corresponding elements (the exhaust grooves) on the upperaxis movable part in an alternative embodiment having two grooves, whenthe movable part is located at a central position (FIG. 5(c)), aleft-most position (FIG. 5(d)) and a right-most position (FIG. 5(e));

[0032]FIG. 6(a) is a sectional view of a static pressure air bearingmechanism according to an alternative embodiment in which the air padsare provided on the upper and lower axes movable parts;

[0033]FIG. 6(b) is a plan view of the inner surface of the upper axismovable part as seen in the direction of arrow B1 in FIG. 6(a);

[0034]FIG. 6(c) is a plan view of the upper surface of the upper axisfixed part as seen in the direction of arrow C1 in FIG. 6(a);

[0035]FIG. 7(a) is a sectional view of a static pressure air bearingmechanism having a different air pad architecture from the FIG. 6(a)embodiment;

[0036]FIG. 7(b) is a plan view of the inner surface of the upper axismovable part as seen in the direction of arrow B2 in FIG. 7(a); and

[0037]FIG. 7(c) is a plan view of the upper surface of the upper axisfixed part as seen in the direction of arrow C2 in FIG. 7(c).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0038] The disclosed static pressure air bearing can be used in variousprecision engineering applications where it is desirable to preciselyposition a workpiece. The workpiece can be, for example, a part to bemachined and/or inspected or a substrate such as a silicon wafer orglass (or quartz) panel on which circuitry is to be formed and/orinspected. For example, the disclosed static pressure air bearing can beused to support a substrate in a photolithography apparatus. In such anapplication, the movable part of the upper axis would typically includea wafer stage and/or chucking apparatus to hold the substrate.

[0039]FIG. 1 is a perspective view showing an embodiment of a staticpressure bearing mechanism according to the present invention. FIGS. 2,2(a), 2(b), 2(f), 2(i) and 2(k) are sectional views showing the junctionof the movable part of the lower axis and the fixed part of the upperaxis of the static pressure bearing mechanism of FIG. 1.

[0040] In both of the figures, air supply tubes 2 and air exhaust pipes3 are connected with lower axis fixed parts 4. The supporting air thatis supplied by the air supply tubes 2 flows through inner air supplypipes (passages) 5 formed within the lower axis fixed parts 4, throughair passages 6, and ultimately is supplied to each of air pads 7 tofloat lower axis movable parts 1. The inner air supply pipes can be seenin FIG. 2(l).

[0041] The supporting air supplied to each of the air pads 7 of thelower axis subsequently flows between the fixed parts 4 and the movableparts 1 and into air exhaust grooves 8 formed in the inner surface ofthe movable parts 1, which extend around the air pads 7 (see FIG. 2(h)).After entering the exhaust grooves 8, the air passes through inner airexhaust pipes (passages) 9 by way of air exhaust tunnels (passages) 20formed within the lower axis fixed parts 4, and ultimately is exhausted(via exhaust pipes 3) outside of the vacuum chamber. The inner airexhaust pipes can be seen in FIG. 2(j).

[0042] The air passages 6 within the lower axis fixed parts 4 branch offin mid course and are communicated with air supply communication grooves13 formed within the lower axis movable parts 1 (see FIG. 2(h)).Further, air passages 19 formed within upper axis fixed part 10 areconnected with the air supply communication grooves 13 through airsupply communication pipes (passages) 14 (see FIG. 2(h)). The lay-out ofthe air pad 7, air passage 6 opening and exhaust tunnel 20 openings onthe upper surface of the lower axis fixed part 4 is shown in FIG. 2(g).Through this structure, a part of the supporting air supplied by the airsupply tubes 2 is supplied to air pads 17 of the upper axis through theair supply communication grooves 13, the air supply communication pipes14, and the air passages 19.

[0043] The supporting air supplied to the air pads 17 of the upper axissubsequently flows into air exhaust grooves 16, which are formed inmovable part 15 of the upper axis. Although not specifically illustratedin FIG. 2, because the air exhaust grooves 16 and the inner air exhaustpipes (passages) 18 formed within the upper axis fixed part 10 areconnected through air exhaust tunnels (31—see FIG. 3, which is across-sectional view of the fixed and movable parts of the upper axis)as is the case with the lower axis, the supporting air that flowed intothe air exhaust grooves 16 is then exhausted outside of the vacuumchamber through the inner air exhaust pipe 18, air exhaust communicationpipes (passages) 12, air exhaust communication grooves 11 and the innerair exhaust pipes 9. In particular, the ends of tunnels 31 defineapertures 31′ in the surface of upper axis fixed part 10, whichcommunicate with the grooves 16 in the upper axis movable part 15. Thestructure of pipes 18 and passages 19 can be appreciated from FIGS. 2(d)and 2(e). FIG. 2(c) shows the locations of the air pad 17 and tunnelapertures 31′ on the surface of the upper axis fixed part 10.

[0044]FIG. 4 is a plan view of the inner surface of one side (of the 4sides) of movable part 15 of the upper axis. As can be appreciated fromFIG. 4, the air exhaust groove 16 extends around the circumference ofthe inner surface of the side of the movable part 15 so as to surroundits corresponding air pad 17 (located on the fixed part 10 of the upperaxis). Accordingly, all air expelled into the air pad 17 will bereceived by air exhaust groove 16, and prevented from entering thevacuum environment in which the air bearing is used. As the movable part15 moves along the fixed part 10, the longitudinal legs 16 a of thegroove 16 remain in communication with the air exhaust tunnels 31 sothat the exhausted air is transmitted through inner air exhaust pipes18, air exhaust communication pipes 12, air exhaust communicationgrooves 11, inner air exhaust pipes 9, and ultimately exhausted throughair exhaust pipes 3.

[0045] The inner surface of each of the four sides of the upper axismovable part 15 have exhaust grooves 16 similar to what is shown in FIG.4. The inner surfaces of each of the four sides of the lower axismovable parts 1 have grooves 8 structured similar to grooves 16 (seeFIGS. 2(h), 5(a) and 5(b)). The grooves 8 and 16 can have a patternother than what is shown in FIG. 4. For example, the end legs 16 b canextend entirely across the inner surface, rather than stopping wherethey intersect the longitudinal legs 16 a.

[0046] As another alternative, two grooves 16 a and 16 b can be providedin a modified upper axis movable part 15′ as shown in FIGS. 5(c)-5(e).Each of the grooves 16 a, 16 b communicates with groups of tunnelapertures 31 b′ and 31 a′, respectively, provided on the upper axisfixed part. This configuration also can include four air pads 17 on eachsurface of the upper axis fixed part. A similar arrangement can beprovided for the lower axis.

[0047] In order to prevent the supporting air from flowing into thevacuum chamber, the movable parts 1 and 15 should remain overlapped withtheir corresponding air pads 7 and 17, respectively. This is illustratedin FIGS. 2(b) and FIGS. 5(a)-5(e). Thus, the range of motion of themovable parts 1 and 15 is somewhat limited. However, by placing the airpads 7, 17 and the exhaust tunnels 20, 31 near the central portion oftheir corresponding fixed parts 4 and 10, respectively, a sufficientlylarge range of motion is achievable. Thus, a bearing mechanism usable ina vacuum environment is realized because, with respect to both the lowerand upper axes, the supporting air does not flow into the vacuum chamberby virtue of the above mechanism.

[0048] FIGS. 6(a)-6(c) and 7(a)-7(c) illustrate embodiments in which theair pads are formed in the movable parts of the lower and upper axes.The arrangements of FIGS. 6(a)-7(c) keep the bearing system in betterbalance during movement of the movable parts of the lower and upperaxes. In these embodiments, the structures relating to the exhaust airis the same as in the FIG. 2 embodiment.

[0049] As shown in FIGS. 6(a) and 7(a) the movable part 1′ of the loweraxis includes air pads 7′. Supply air is provided to the air pads 7′ viapassages 27′ provided in the movable parts 1′. The passages 27′ receivethe supply air from air supply communication grooves 13 which, asdiscussed previously, communicate with inner air supply pipes 5.

[0050] As can be seen from FIGS. 6(c) and 7(c), the surfaces of theupper axis fixed part 10-1 or 10-2 include exhaust tunnel apertures 31′as in the previous embodiments, but do not include air pads. Rather, anair supply aperture 19′, which is an outlet of air passages 19 in theupper axis fixed parts, is provided.

[0051] In the embodiment of FIGS. 6(a)-6(c), the supply air emitted fromapertures 19′ is received in air supply communication grooves 37′ of themovable part 15-1. The air then travels through air passages 19″ in themovable part 15-1 until reaching the air pads 17-1. In the embodiment ofFIGS. 7(a)-7(c), the air from apertures 19′ is emitted into air supplycommunication grooves 37″, and then into the air pads 17-2 of the upperaxis movable part 15-2.

[0052] Because of the design of a static pressure air bearing having twoaxes usable in a vacuum environment in which the air exhaust pipes areconnected only with the fixed parts of the lower axis and need not beconnected with the movable parts of the bearing mechanism, air exhaustpipes having a large bore diameter do not adversely affect the bearingperformance, e.g., rectilinear feeding accuracy.

[0053] The supporting air and the exhaust air for the upper axis can beconveyed to the upper axis through one or both of the lower axis movableparts 1. The term “air” as used herein is intended to cover any fluidthat is suitable for use in a static air bearing, and is not intended tobe limited to strictly atmospheric air.

[0054] While the present invention has been described with reference topreferred embodiments thereof, it is to be understood that the inventionis not limited to the disclosed embodiments or constructions. To thecontrary, the invention is intended to cover various modifications andequivalent arrangements. In addition, while the various elements of thedisclosed invention are shown in various combinations andconfigurations, which are exemplary, other combinations andconfigurations, including more, less or only a single element, are alsowithin the spirit and scope of the invention.

What is claimed is:
 1. A static pressure air bearing comprising: a first axis having a fixed part and a movable part that is movably mounted to the fixed part, the fixed part including a first exhaust passage; and a second axis having a fixed part and a movable part that is movably mounted to the fixed part of the second axis, the fixed part of the second axis attached to the movable part of the first axis and including a second exhaust passage in communication with the first exhaust passage.
 2. A static pressure air bearing according to claim 1, wherein the movable part of the first axis includes an exhaust communication passage that communicates the first exhaust passage of the first axis fixed part with the second exhaust passage of the second axis fixed part.
 3. A static pressure air bearing according to claim 2, wherein supporting air that forms air pads between the fixed and movable parts of the first axis and between the fixed and movable parts of the second axis is exhausted through the first and second exhaust passages.
 4. A static pressure air bearing according to claim 1, wherein supporting air that forms air pads between the fixed and movable parts of the first axis and between the fixed and movable parts of the second axis is exhausted through the first and second exhaust passages.
 5. A static pressure air bearing according to claim 4, wherein external surfaces of the fixed parts of the first and second axes include exhaust orifices that communicate with respective ones of the first and second exhaust passages, and internal surfaces of the movable parts of the first and second axes include air exhaust grooves that communicate with respective ones of the exhaust orifices in the fixed parts of the first and second axes.
 6. A static pressure air bearing according to claim 1, wherein external surfaces of the fixed parts of the first and second axes include exhaust orifices that communicate with respective ones of the first and second exhaust passages, and internal surfaces of the movable parts of the first and second axes include air exhaust grooves that communicate with respective ones of the exhaust orifices in the fixed parts of the first and second axes.
 7. A static pressure air bearing according to claim 2, wherein external surfaces of the fixed parts of the first and second axes include exhaust orifices that communicate with respective ones of the first and second exhaust passages, and internal surfaces of the movable parts of the first and second axes include air exhaust grooves that communicate with respective ones of the exhaust orifices in the fixed parts of the first and second axes.
 8. A static pressure air bearing according to claim 7, wherein the fixed part of the first axis includes a first air supply passage, and the fixed part of the second axis includes a second air supply passage in communication with the first air supply passage.
 9. A static pressure air bearing according to claim 1, wherein the fixed part of the first axis includes a first air supply passage, and the fixed part of the second axis includes a second air supply passage in communication with the first air supply passage.
 10. A static pressure air bearing according to claim 2, wherein the fixed part of the first axis includes a first air supply passage, and the fixed part of the second axis includes a second air supply passage in communication with the first air supply passage.
 11. A static pressure air bearing according to claim 4, wherein the fixed part of the first axis includes a first air supply passage, and the fixed part of the second axis includes a second air supply passage in communication with the first air supply passage.
 12. A static pressure air bearing according to claim 11, wherein the movable part of the first axis includes an air supply communication passage that communicates the first air supply passage of the first axis fixed part with the second air supply passage of the second axis fixed part.
 13. A static pressure air bearing according to claim 8, wherein the movable part of the first axis includes an air supply communication passage that communicates the first air supply passage of the first axis fixed part with the second air supply passage of the second axis fixed part.
 14. A static pressure air bearing according to claim 9, wherein the movable part of the first axis includes an air supply communication passage that communicates the first air supply passage of the first axis fixed part with the second air supply passage of the second axis fixed part.
 15. A static pressure air bearing according to claim 10, wherein the movable part of the first axis includes an air supply communication passage that communicates the first air supply passage of the first axis fixed part with the second air supply passage of the second axis fixed part.
 16. A method of making a static pressure air bearing comprising the steps of: providing a first axis having a fixed part and a movable part that is movably mounted to the fixed part, the fixed part including a first exhaust passage; and providing a second axis having a fixed part and a movable part that is movably mounted to the fixed part of the second axis, the fixed part of the second axis attached to the movable part of the first axis and including a second exhaust passage in communication with the first exhaust passage.
 17. A method according to claim 16, wherein the movable part of the first axis includes an exhaust communication passage that communicates the first exhaust passage of the first axis fixed part with the second exhaust passage of the second axis fixed part.
 18. A method according to claim 16, wherein supporting air that forms air pads between the fixed and movable parts of the first axis and between the fixed and movable parts of the second axis is exhausted through the first and second exhaust passages.
 19. A method according to claim 16, wherein external surfaces of the fixed parts of the first and second axes include exhaust orifices that communicate with respective ones of the first and second exhaust passages, and internal surfaces of the movable parts of the first and second axes include air exhaust grooves that communicate with respective ones of the exhaust orifices in the fixed parts of the first and second axes.
 20. A method according to claim 16, wherein the fixed part of the first axis includes a first air supply passage, and the fixed part of the second axis includes a second air supply passage in communication with the first air supply passage.
 21. A method according to claim 20, wherein the movable part of the first axis includes an air supply communication passage that communicates the first air supply passage of the first axis fixed part with the second air supply passage of the second axis fixed part.
 22. A method of exhausting supporting air from a two-axis static pressure air bearing that includes a first axis having a fixed part and a movable part that is movably mounted to the fixed part, and a second axis having a fixed part and a movable part that is movably mounted to the fixed part of the second axis, the fixed part of the second axis attached to the movable part of the first axis, the method comprising the step of: exhausting the supporting air from air pads located between the fixed and movable parts of the second axis through a first exhaust passage located in the fixed part of the first axis and a second exhaust passage located in the fixed part of the second axis, the second exhaust passage in communication with the first exhaust passage.
 23. A method according to claim 22, wherein the movable part of the first axis includes an exhaust communication passage that communicates the first exhaust passage of the first axis fixed part with the second exhaust passage of the second axis fixed part.
 24. A method according to claim 22, wherein external surfaces of the fixed parts of the first and second axes include exhaust orifices that communicate with respective ones of the first and second exhaust passages, and internal surfaces of the movable parts of the first and second axes include air exhaust grooves that communicate with respective ones of the exhaust orifices in the fixed parts of the first and second axes.
 25. A method according to claim 22, further comprising the step of supplying the supporting air to the air pads between the fixed and movable parts of the second axis through a first air supply passage located in the fixed part of the first axis and a second air supply passage located in the fixed part of the second axis and in communication with the first air supply passage.
 26. A method according to claim 25, wherein the movable part of the first axis includes an air supply communication passage that communicates the first air supply passage of the first axis fixed part with the second air supply passage of the second axis fixed part. 